Recently, vehicles, such as a truck, running while loaded with heavy goods, have been regarded as having problems that the vehicle brings about a traffic accident, such as lateral turning, and that the vehicle and the road surface are subjected to extremely-premature deterioration.
One cause of these problems is overloadage, and in order to prevent this overloadage; the load, carried by the vehicle, that is, the load acting on the vehicle, has heretofore been measured.
The load, carried by the vehicle, has heretofore been measured while placing the vehicle to be measured on a platform scale called a truck weight scale. However, this facility is large, and requires a large installation space, and therefore the number of the platform scales, that can be installed, is limited, and many vehicles can not be measured, and besides the installation cost is high.
Therefore, recently, there has been provided a load measuring apparatus which is mounted on the vehicle so as to measure the load.
For example, in Japanese Patent Application No. Hei. 7-124860 proposed by the present applicant, attention is directed to the fact that a shackle 34 is provided between one end of a leaf spring 31 (the other end of which is connected to a bed frame 32 through a bifurcated bracket 33) and another bracket 33 connected to the bed frame 32, as shown in FIG. 12 which is a perspective view, and a load-measuring sensing device of the strain gauge type, such as a strain gauge type sensor, is mounted in a shackle pin 5 which rotatably connects the shackle 34 to the bracket 33, and the load is calculated based on the sum of values measured by the plurality of sensing devices corresponding to wheels.
FIG. 13 is a cross-sectional view showing the arrangement of the sensing device within the shackle pin, and receiving portions 5a and 5b are formed respectively in axial end portions of the shackle pin 5, and the two receiving portions 5a and 5b communicate with each other through a communication hole 5c within the shackle pin 5.
Within one receiving portion 5a of the shackle pin 5, the sensing device 7 is received in a first case assembly 9, and within the other receiving portion 5b of the shackle pin 5, the sensing device 7 is received in a second case assembly 11.
As shown in FIG. 14 which is a perspective view, each of the conventional sensing devices 7, received respectively in the two receiving portions 5a and 5b of the shackle pin 5, includes a plate-like member 7a, and a coil 7g serving as a sensing portion.
The plate-like member 7a is made of a magnetic material such as permalloy, and has a substantially rectangular, flattened shape as seen in a plan view, and includes a coil portion 7b disposed at a substantially longitudinally-central portion thereof, and fixing portions 7c and 7c defined respectively by opposite end portions thereof. Notches 7e of a substantially semi-circular shape for alleviating stresses acting on the plate-like member 7a are formed respectively in four portions of opposite edges of the plate-like member 7a spaced from each other in a widthwise direction perpendicular to the above longitudinal direction, and these four portions are disposed respectively at the boundaries between the coil portion 7b and the two fixing portions 7c and 7c. Four through-holes 7f are formed through the coil portion 7b delimited by the four notches 7e, and are spaced from one another in the longitudinal and widthwise directions.
The coil 7g includes two magnet wires 7h constituting a cross coil, and these magnet wires 7h are coated with an insulating material (not shown) such as enamel.
One of the two magnet wires 7h is wound through the two through-holes 7f and 7f opposed to each other in the longitudinal direction, and its opposite end portions are extended outwardly from the two through-holes 7f and 7f, respectively. The other magnet wire 7h is wound through the two through-holes 7f and 7f opposed to each other in the widthwise direction, and its opposite end portions are extended outwardly from the two through-holes 7f and 7f, respectively.
The sensing devices 7 of this construction are received respectively in the first case assembly 9 and the second case assembly 11, and in this condition these sensing devices are received respectively in the two receiving portions 5a and 5b of the shackle pin 5 normally in such a posture (as shown in FIG. 13) that the longitudinal direction of the plate-like member 7a is disposed in the direction of the axis of the shackle pin 5 extending in a direction B of a width of a vehicle while the widthwise direction of the plate-like member 7a is disposed in a direction A of a height of the vehicle, and one fixing portion 7c is associated with the bracket 33 while the other fixing portion 7c is associated with the shackle 34.
In this condition, the axis of winding of the magnet wire 7h, wound through the two through-holes 7f and 7f opposed to each other in the longitudinal direction of the plate-like member 7a, and the axis of winding of the magnet wire 7h, wound through the two through-holes 7f and 7f opposed to each other in the widthwise direction of the plate-like member 7a, are both disposed in a plane including the longitudinal direction and widthwise direction of the plate-like member 7a, that is, in a plane including the direction A of the height of the vehicle and the direction B of the width of the vehicle.
In the sensing device 7, when electric current is caused to flow either between the opposite ends of one magnet wire 7h, wound through the two through-holes 7f and 7f opposed to each other in the longitudinal direction of the plate-like member 7a, or between the opposite ends of the magnet wire 7h, wound through the two through-holes 7f and 7f opposed to each other in the widthwise direction of the plate-like member 7a, a magnetic field is produced in the plate-like member 7a, so that induced current flows between the opposite ends of the other magnet wire 7h.
In this condition, the load is applied to the plate-like member 7a from the bed frame 32 through the bracket 33, the shackle 34 and the opposite ends of the shackle pin 5, and the bracket 33 is moved relative to the shackle 34 in the direction A of the height of the vehicle, so that the plate-like member 7a is strained in the direction A of the height of the vehicle, and at this time the direction of the magnetic field in the plate-like member 7a is changed, so that the induced current, flowing between the opposite ends of the other magnet wire 7h, is changed.
Therefore, the current, having a magnitude corresponding to the load acting on the plate-like member 7a, is obtained as an output signal from the opposite ends of the other magnet wire 7h.
Incidentally, the above-mentioned problems that the vehicle brings about a traffic accident, such as lateral turning, and that the vehicle and the road surface are subjected to extremely-premature deterioration are not always caused by the overloadage of the vehicle, and these problems can occur also when the acceleration and deceleration are effected abruptly with a considerable loaded weight.
Therefore, in a vehicle such as a truck, it is desirable to measure a change of the load in a forward-backward direction C (see FIG. 12) of the vehicle so that the acceleration/deceleration can be grasped together with the load.
However, the above conventional sensing device 7 is originally provided for the purpose of detecting only the load, that is, the loaded weight, acting in the direction A of the height of the vehicle, and therefore when the sensing device is mounted in the shackle pin 5, the axes of winding of the two magnet wires 7h and 7h, constituting the coil 7g, extend in the direction A of the height of the vehicle and the direction B of the width of the vehicle (which is the direction of the axis of the shackle pin 5), respectively, and therefore only changes of the load in the direction A of the height and the direction B of the vehicle width can be measured, and in order to measure a change of the load in the forward-backward direction of the vehicle, other sensor than the sensing devices 7 must be provided.
Thus, the conventional sensing device 7 of the strain gauge type has a disadvantage that it can not simultaneously detect changes of a load, acting on a vehicle, in two different directions.
This invention has been made under the above circumstances, and an object of the invention is to provide a sensing device of the strain gauge type which is capable of detecting changes of a load on a vehicle in two directions simultaneously by itself.